1. Technical Field of the Invention
This invention relates generally to high frequency signal processing and more particularly to wireless communications.
2. Description of Related Art
As is known, a good ground connection (i.e., one that provides a stable low impedance path) is an important aspect to reduce noise interferences in many analog and mixed signal circuits. In circuits that include integrated circuits (IC) and a printed circuit board (PCB), the IC must include a good internal ground connection and the PCB must also have a good ground connection. Typically, a PCB will include a ground plane and thick traces to provide its ground path.
As is further known, an IC includes a die and a package that supports the die. The die typically includes a ground plane and thick traces to provide its ground path, however, the size of the die's ground plane and thick traces will be significantly smaller than the corresponding ground connection of the PCB. The package includes a plurality of IC pins that are coupled via bond wires to input/output connections of the die, which include the ground connection. The plurality of pins is also coupled to pads on the PCB such that the circuitry of the die is operably coupled to circuitry on the PCB.
As is also known, an electrical model of a PCB trace, an IC trace, and/or a bond wire may be at least partially represented as a series resistor and a series inductor. The values of the series resistor and the series inductor are directly dependent on the thickness and length of the trace and/or wire. For instance, the resistance of the series resistor and the inductance of the series inductor decrease as the thickness of the trace or wire increases and as the length of the trace or wire decreases. Based on these physical properties of the traces and/or bond wires, the impedance is readily determined as R+2πfL, where R is the resistance of the series resistance, f is the frequency of the signal traversing the trace or wire, and L is the inductance of the series inductor.
Due to physical limitations, the thickness and length of IC traces and bond wires can only be so thick and can only be so short. Thus, as the frequency of the signals that traverse the IC traces and/or bond wires increase, the impedance of the trace and/or bond wire becomes a factor is circuit design. For instance, if a bond wire has a 2 nano Henry (nH) series inductance and the signal traversing the bond wire has a frequency of 2.4 giga Hertz (GHz), the impedance of the series inductor is 2π*(2.4 GHz)*(2 NH), which equals approximately 30 Ohms. If the bond wire is coupling a ground connection of a die to an IC pin, which, in turn, is coupled to a ground connection on the PCB, the impedance will adversely affect the performance of the circuit.
One solution to the above problem is to use multiple bond wires connected in parallel to reduce the effective series impedance. While this solution reduces the impedance at high frequencies, it requires multiple pads on the die, multiple IC pins on the package, and multiple pads on the PCB. By increasing the number of pads on the die and increases the pin count of the package, the cost of the IC will increase.
Therefore, a need exists for a grounding system that minimizes pin count and die pad connections while providing a good ground connection.